With the K5, you can easily go with option A since you can still bump your ISO up if you need more light and still be able to take advantage of 18-55mm weather resistant as well as the zoom range of 55-300mm. Believe me, you will find the 55-300mm still suitable for your street photography (now you have the reach!) You can also check the other Pentax forum and see how you can get higher ISO shoot without noise. I've been trying that setting with my K7 and get a very good image capture at ISO 3200. Your K5 will bring you more than that for sure!